“Friends of Lord Darzi said he was exhausted from holding two jobs and had done what he had set out to do and put the NHS on the path to reform. “He was trying to be a minister and an innovative surgeon at the same time – it’s knackering,” said one friend.”

“Colleagues were puzzled over the timing of his decision to leave but the squeeze on public spending would have made implementing his agenda more difficult. A source said: “There was always an understanding he would do the [quality] report, do the one-year review and then see where things were going from there.”

“Last month Lord Darzi told HSJ there was “absolutely” no substance to rumours he has been unhappy with the political aspect of his role.

Asked what he would be doing this time next year, he made it clear he expected not to be a minister: “The people who will make change in the NHS are not here [in the Department of Health], they are out there. And I will be with them doing my work.”

“In a statement, Downing Street said the prime minister had thanked him for an “outstanding contribution” as a health minister.

“He will take on a new role as a health and life sciences ambassador for the government and will chair a new NHS Global forum to promote the NHS and the UK’s life-sciences industry around the world,” it said.

“Lord Darzi will also advise on health reforms in both the NHS and our global public health.”